Cooling issues in semiconductor elements mounted in various electronic/electric instruments such as computers, and in other heat-generating components have been emphasized. As a cooling method of such components which should be cooled, a method including attaching a fan to an instrument housing in which the component is mounted, thereby cooling the instrument housing; a method including attaching a heat conductor such as a heat pipe, a heat spreader, a heat sink or a fin to the component to be cooled, thereby cooling is executed by transferring outward the heat from the element; or the like may be generally employed. Examples of a heat-conducting material attached to a component which should be cooled include aluminum plates, copper plates, and the like. In such a case, a heat-generating component is attached to a part of the aluminum or copper plate, or to the heat pipe, whereby further heat dissipation of other portion of the plate is allowed outside using a fin or a fan.
Meanwhile, downsizing of each instrument into which a heat-generating component such as a semiconductor element is mounted has been performed in recent years, and the amount of heat generation of the member thereof tends to be larger. However, due to downsizing of the housing, the space into which a component such as a fin or a heat sink, a fan and the like can be inserted has been limited.
Thus, graphite films that are excellent in thermal diffusivity have been regarded as a promising heat conductor in recent years. A graphite film has a layered structure formed with carbon, and is a material having a very high thermal conductivity in the face thereof, having a density of the film being approximately 1 to 2 g/cm3, thus being light, and having a high electric conductivity. In addition since the sheet can be thinned in the thickness and is flexible, it is expected as a heat conductor material or a heat spreader material for use in narrow places, or places in which affixing around through gaps is required.
For the present, commonly available graphite films may be exemplified by graphite films manufactured by a polymer thermal degradation method or an expansion method.
The polymer thermal degradation method is, as disclosed in Patent Documents 1 and 2, a method in which a polymer film of polyoxadiazole, polyimide, polyphenylenevinylene, polybenzoimidazole, polybenzooxazole, polythiazole, polyamide or the like is subjected to a heat treatment in an inert atmosphere of argon, helium or the like, or under reduced pressure, whereby a graphite film is obtained.    Patent Document 1: JP-A No. Sho 61-275116    Patent Document 2: JP-A No. He 2-103478On the other hand, the graphite is obtained by immersing powdery or squamous natural black lead, which is used as a source material, in an acid and thereafter widening the space between the graphite layers by heating, in an expansion method. Additionally, high-pressure press processing is carried out with a caking additive, thereby yielding a filmy graphite.